The invention relates to a rocker am for a valve train of an internal combustion engine having a cam contacting surface for a cam support, a recess for a hydraulic valve-play adjusting element, and a rocker arm shaft located therebetween.
Rocker arms of conventional design are manufactured by the Croning method, and subjected to special heat treatment to produce a hard cam contacting surface. A recess in the form of above for receiving a hydraulic valve-play adjusting element is then provided in the rocker arm.
One object of the present invention is to provide a rocker arm that can be manufactured simply using the Croning method casting, but without costly machining.
This goal is achieved by the rocker arm according to the invention which is made by the Croning casting method and consists of higher-strength cast iron. It has a much greater hardness in the vicinity of its cam contacting surface than in the vicinity of the recess for the hydraulic valve-play adjusting element, or near the rocker armshaft bearing and the oil supply bore. The higher-strength cast iron, after pouring, consists of a chilled cast iron in the vicinity of the cam contacting surface, and a nodular cast iron in the vicinity of the rocker arm shaft bearing up to the recess for the valve-play adjusting element. In the vicinity of the cam contacting surface, the structure of the rocker arm consists of ledeburite and a small quantity of nodular graphite, and is relatively hard. This arrangement eliminates the need for additional machining or the addition of a hardened plate.
The area around the rocker arm shaft bearing up to the recess consists of a structure composed of perlite, ferrite, and nodular graphite, so that the material is softer than the cam contacting surface. This soft area of the rocker arm is necessary in order to permit accurate drilling of the recess without a great deal of expenditure of labor, and drilling of a lubricating bore from the rocker arm axis to the recess in simple fashion.
The recess has a relatively thin wall and is produced during casting by a core insert, so that subsequent machining is inexpensive, and considerably simplified. The area around the recess for the rocker arm has a perlite-ferrite-nodular graphite structure, so that despite the relatively thin walls, the recess has a wall thickness that can correspond roughly to one-third of the radius of the receiving bore in the rocker arm, which is favorable from the standpoint of weight.
The different degrees of hardness of the rocker arm and the cam contacting surface, starting from one free end and extending up to the recess at the other free end of the rocker arm are produced by casting. The harder area of the rocker arm in the cam contacting area, produced in chilled cast iron, is produced by means of a densener which disposed adjacent this surface during the casting process, so that this area of the rocker arm solidifies more rapidly than the remaining part around the shaft and the recess for the rocker arm.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.